A mysterious case involving two suspicious characters forced a Hawaiian Airlines flight to turn back last week, while another Hawaiian flight, this one originating in Australia, had to divert over a tragedy involving a toddler.

A Hawaiian flight heading from Sydney to Honolulu diverted to Fiji after a toddler suffered an emergency medical problem during the flight. Crewmembers did everything they could, but tragically the child died.

The plane arrived in Fiji at night and no airport crew was available to push it back. The flight later continued to Honolulu.

Not long beforehand, a Hawaiian Airlines flight heading from Honolulu to South Korea turned back over concerns about two mysterious passengers. Both were said to be acting suspiciously.

The FBI said two passengers were detained and interviewed after the plane landed. They were subsequently released and no charges were laid. Despite much speculation, mystery surrounds quite what the passengers were doing, or whether they were doing it together.

“Our investigation indicates that the incident in question was not an intentional threat to the crew or passengers on board the plane,” the FBI said, in an issued statement.

Some 285 passengers on the aircraft were able to depart for South Korea on a different plane.